I bought 2 laptops Teclast F7 plus on Amazon for my kids and after 1 year got exactly the same problem than you on both laptops! $800 to the trash!!!!
When I hit the power button it lights up for a second and then turn definitely OFF.
I wrote to Amazon and they answered that they don’t work anymore with Teclast so I had to manage it directly with them but Teclast does NOT have any customer service at all and don’t want to fix the problem.
I swapped the power adaptor, the battery, the SSD, tried to reset everything, pushing the power button several minutes and no change.
Sometimes, after a couple of days/weeks without doing anything, one of the laptop starts again but stops again after few seconds.
Does anyone found a solution to fix this problem?